Growing on the top of a sandstone wall
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
As I said in another observation, I would only use the term "chewing gum lichen" when the lichen thallus is on pavement and looking like trodden chewing gum.
In this case it is on the top of a wall, and is a pretty typical rounded thallus as formed by numerous crustose species.
It seems to be a Lecanora or Lecania, but puzzling (to me). I would want to check microscopic characters before speculating.
Or perhaps I will speculate after all. The best candidate seemed to be Lecanora campestris and I have just been looking at some photographs I have of a diseased colony of this species. I think there is a match to the photograph here.
Even so, I think the ID is best left as Lecanora (genus).
Lat/Lng: 51.4739, -2.5857
OS grid ref: ST594751